Climate Change & Anthropocene Extinction 30: Heavy breathing tropical forests under record heat

Today the WMO announced that the atmospheric CO2 concentration last year rose at a record high speed: +3.3 ppm – jumping from 400.0 ppm in 2015 to 403.3 in 2016. The annual average rise is close to 2 ppm.

A few days earlier NASA scientists had explained why the global CO2 rise has suddenly rapidly accelerated: rainforests across Earth’s tropics, suffering unprecedented heat and drought, and exhaling a massive amount of CO2 (9.2 billion tonnes) – adding over 50 percent to the global fossil fuelled economy:

tropical forests CO2 source climate change
During the global heat records of 2015 and 2016 tropical rainforests across South America, Africa and Southeast Asia all independently became net CO2 emitters. Although part of this pattern can be associated with El Niño-drought (for instance Borneo and Sumatra) and therefore natural climate variability, what is unusual is the geographical scale – and the fact that temperature played an independent role, next to (local) droughts.

NASA derived the specific location-bound CO2 emissions data from a new climate satellite – Orbiting Carbon Observatory-2, or ‘OCO-2′ – and published its maiden-flight results in Science earlier this month, in a publication titled ‘Contrasting carbon cycle responses of the tropical continents to the 2015–2016 El Niño’.

Thanks to a different climate satellite project, the European Copernicus Atmosphere Monitoring Service, we already knew in late 2015 that tropical rainforests showed a rather unusual response to the strong late-2015 El Niño. Normally El Niño leads to drought in the West Pacific and around the Indonesian Islands, fuelling forest fires in Australia, Papua New Guinea, Borneo and Sumatra – and a subsequent rise in CO2 emissions for burning peat forests. But in late 2015 not just the forests of Southeast Asia, but also the Amazon suffered a very strong drought – and judging by live satellite images of the time, even higher CO2 emissions there.

The new publication shows in following months it became a pantropical response, as large-scale forest degradation CO2 emissions continued – with the three main tropical continents contributing about equal amounts, albeit from different dominant processes. Especially the African forests’ response is remarkable, because these forests became net emitters not as a result of drought – but of direct heat stress.

And there the new study may hold a true climatic warming, one that goes beyond natural El Niño variability: if the temperature rises, you don’t even need to also have a precipitation decline to experience forest degradation. Sometimes heat is powerful enough to do that job on its own. That’s worrying, for instance considering Africa’s general climate outlook – and an increasing total tropical forest carbon store that may climatically unstable.

© Rolf Schuttenhelm | www.bitsofscience.org

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